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Some thoughts - mostly philosophical

What are white dwarfs?

Some curiosities about white dwarfs, a stellar corpse and the future of the sun.

Where a star ends up at the end of its life depends on the mass it was born with. Stars that have a lot of mass may end their lives as black holes or neutron stars.

A white dwarf is what stars like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a planetary nebula.

In 5.4 billion years from now, the Sun will enter what is known as the Red Giant phase of its evolution. This will begin once all hydrogen is exhausted in the core and the inert helium ash that has built up there becomes unstable and collapses under its own weight. This will cause the core to heat up and get denser, causing the Sun to grow in size.

It is calculated that the expanding Sun will grow large enough to encompass the orbit’s of Mercury, Venus, and maybe even Earth.

A typical white dwarf is about as massive as the Sun, yet only slightly bigger than the Earth. This makes white dwarfs one of the densest forms of matter, surpassed only by neutron stars and black holes.

The gravity on the surface of a white dwarf is 350,000 times that of gravity on Earth. 

White dwarfs reach this incredible density because they are so collapsed that their electrons are smashed together, forming what is called “degenerate matter.” This means that a more massive white dwarf has a smaller radius than its less massive counterpart. Burning stars balance the inward push of gravity with the outward push from fusion, but in a white dwarf, electrons must squeeze tightly together to create that outward-pressing force. As such, having shed much of its mass during the red giant phase, no white dwarf can exceed 1.4 times the mass of the sun.

While many white dwarfs fade away into relative obscurity, eventually radiating away all of their energy and becoming a black dwarf, those that have companions may suffer a different fate.

If the white dwarf is part of a binary system, it may be able to pull material from its companion onto its surface. Increasing the mass can have some interesting results.

One possibility is that adding more mass to the white dwarf could cause it to collapse into a much denser neutron star.

A far more explosive result is the Type 1a supernova. As the white dwarf pulls material from a companion star, the temperature increases, eventually triggering a runaway reaction that detonates in a violent supernova that destroys the white dwarf. This process is known as a single-degenerate model of a Type 1a supernova. 

If the companion is another white dwarf instead of an active star, the two stellar corpses merge together to kick off the fireworks. This process is known as a double-degenerate model of a Type 1a supernova.

At other times, the white dwarf may pull just enough material from its companion to briefly ignite in a nova, a far smaller explosion. Because the white dwarf remains intact, it can repeat the process several times when it reaches the critical point, briefly breathing life back into the dying star over and over again. 

Image credit: www.aoi.com.au/ NASA/ ESA/ Hubble/  Wikimedia Commons/ Fsgregs/ quora.com/ quora.com/ NASA’s Goddard Space Flight Center/S. Wiessinger/ ESO/ ESO/ Chandra X-ray Observatory

Source: NASA/ NASA/ space.com

Black Holes are NICER Than You Think!

We’re learning more every day about black holes thanks to one of the instruments aboard the International Space Station! Our Neutron star Interior Composition Explorer (NICER) instrument is keeping an eye on some of the most mysterious cosmic phenomena.

We’re going to talk about some of the amazing new things NICER is showing us about black holes. But first, let’s talk about black holes — how do they work, and where do they come from? There are two important types of black holes we’ll talk about here: stellar and supermassive. Stellar mass black holes are three to dozens of times as massive as our Sun while supermassive black holes can be billions of times as massive!

Stellar black holes begin with a bang — literally! They are one of the possible objects left over after a large star dies in a supernova explosion. Scientists think there are as many as a billion stellar mass black holes in our Milky Way galaxy alone!

Supermassive black holes have remained rather mysterious in comparison. Data suggest that supermassive black holes could be created when multiple black holes merge and make a bigger one. Or that these black holes formed during the early stages of galaxy formation, born when massive clouds of gas collapsed billions of years ago. There is very strong evidence that a supermassive black hole lies at the center of all large galaxies, as in our Milky Way.

Imagine an object 10 times more massive than the Sun squeezed into a sphere approximately the diameter of New York City — or cramming a billion trillion people into a car! These two examples give a sense of how incredibly compact and dense black holes can be.

Because so much stuff is squished into such a relatively small volume, a black hole’s gravity is strong enough that nothing — not even light — can escape from it. But if light can’t escape a dark fate when it encounters a black hole, how can we “see” black holes?

Scientists can’t observe black holes directly, because light can’t escape to bring us information about what’s going on inside them. Instead, they detect the presence of black holes indirectly — by looking for their effects on the cosmic objects around them. We see stars orbiting something massive but invisible to our telescopes, or even disappearing entirely!

When a star approaches a black hole’s event horizon — the point of no return — it’s torn apart. A technical term for this is “spaghettification” — we’re not kidding! Cosmic objects that go through the process of spaghettification become vertically stretched and horizontally compressed into thin, long shapes like noodles.

Scientists can also look for accretion disks when searching for black holes. These disks are relatively flat sheets of gas and dust that surround a cosmic object such as a star or black hole. The material in the disk swirls around and around, until it falls into the black hole. And because of the friction created by the constant movement, the material becomes super hot and emits light, including X-rays.  

At last — light! Different wavelengths of light coming from accretion disks are something we can see with our instruments. This reveals important information about black holes, even though we can’t see them directly.

So what has NICER helped us learn about black holes? One of the objects this instrument has studied during its time aboard the International Space Station is the ever-so-forgettably-named black hole GRS 1915+105, which lies nearly 36,000 light-years — or 200 million billion miles — away, in the direction of the constellation Aquila.

Scientists have found disk winds — fast streams of gas created by heat or pressure — near this black hole. Disk winds are pretty peculiar, and we still have a lot of questions about them. Where do they come from? And do they change the shape of the accretion disk?

It’s been difficult to answer these questions, but NICER is more sensitive than previous missions designed to return similar science data. Plus NICER often looks at GRS 1915+105 so it can see changes over time.

NICER’s observations of GRS 1915+105 have provided astronomers a prime example of disk wind patterns, allowing scientists to construct models that can help us better understand how accretion disks and their outflows around black holes work.

NICER has also collected data on a stellar mass black hole with another long name — MAXI J1535-571 (we can call it J1535 for short) — adding to information provided by NuSTAR, Chandra, and MAXI. Even though these are all X-ray detectors, their observations tell us something slightly different about J1535, complementing each other’s data!

This rapidly spinning black hole is part of a binary system, slurping material off its partner, a star. A thin halo of hot gas above the disk illuminates the accretion disk and causes it to glow in X-ray light, which reveals still more information about the shape, temperature, and even the chemical content of the disk. And it turns out that J1535’s disk may be warped!

Image courtesy of NRAO/AUI and Artist: John Kagaya (Hoshi No Techou)

This isn’t the first time we have seen evidence for a warped disk, but J1535’s disk can help us learn more about stellar black holes in binary systems, such as how they feed off their companions and how the accretion disks around black holes are structured.

NICER primarily studies neutron stars — it’s in the name! These are lighter-weight relatives of black holes that can be formed when stars explode. But NICER is also changing what we know about many types of X-ray sources. Thanks to NICER’s efforts, we are one step closer to a complete picture of black holes. And hey, that’s pretty nice!

Make sure to follow us on Tumblr for your regular dose of space: http://nasa.tumblr.com.

Great brief and wonderful pic!

This NASA/ESA Hubble Space Telescope image is chock-full of galaxies. Each glowing speck is a different galaxy, except the bright flash in the middle of the image which is actually a star lying within our own galaxy that just happened to be in the way. At the center of the image lies something especially interesting, the center of the massive galaxy cluster called WHL J24.3324-8.477, including the brightest galaxy of the cluster.

The Universe contains structures on various scales — planets collect around stars, stars collect into galaxies, galaxies collect into groups, and galaxy groups collect into clusters. Galaxy clusters contain hundreds to thousands of galaxies bound together by gravity. Dark matter and dark energy play key roles in the formation and evolution of these clusters, so studying massive galaxy clusters can help scientists to unravel the mysteries of these elusive phenomena.

Credit: ESA/Hubble & NASA

30 years after the detection of SN1987A neutrinos

On February 23, 1987, just before 30 years from today, the neutrinos emitted from the supernova explosion SN1987A in the Large Magellanic Cloud, approximately 160,000 light-years away, reached the earth. Kamiokande, the predecessor detector of Super-Kamiokande, detected the 11 emitted neutrinos. Worldwide, it was the first instance of the detection of the emitted neutrinos from the supernova burst, and it served a big step toward resolving the supernova explosion system. In 2002, Dr. Masatoshi Koshiba, a Special University Professor Emeriuts of the University of Tokyo, was awarded a Nobel Prize in Physics for this achievement.

Before the explosion of supernova SN1987A (right) and after the explosion (left) Anglo-Australian Observatory/David Malin

Kamiokande, the pioneer of neutrino research

Kamiokande detector was a cylindrical water tank (16 m in diameter and height) with 1000 of the world’s largest photomultiplier tubes inside it, and it was laid 1000 m underground in Kamioka-town, Yoshiki-gun, (currently Hida-city) Gifu Prefecture, Japan. (Currently the site of Kamiokande is used for KamLAND experiment.) Kamiokande was devised by Prof. Koshiba who started the observation in 1983. Originally, it was constructed for detecting the proton decay phenomenon, but it was modified for the solar neutirno observation. By the end of 1986, the detector modification was completed and the observation began.

Inside of Kamiokande detector

Overview of Kamiokande detector

Prof. Koshiba working in the tank

Prof. Kajita and Prof. Nakahata (then PhD students) tuning up the data aquision system in the mine

The day of detection of the supernova neutrinos

On February 25, 1987, two days after the observation of supernova SN1987A through naked eyes, a fax was sent from Pennsylvania University to the University of Tokyo to inform them about the supernova explosion. Soon after receiving the fax, Prof. Yoji Totsuka asked the researcher in Kamioka to send the magnetic tapes that recorded the Kamiokande data. (At that time, the information network was not developed, so the data was delivered physically).

The fax sent from Pennsylvania University to inform about the supernova explosion.

On February 27, when the magnetic tapes arrived at the laboratory in Tokyo, Prof. Masayuki Nakahata (currently the spokesperson of Super-Kamiokande experiment), who was then a PhD student immediately started the analysis. On the morning of February 28, while Prof. Nakahata printed out the analysis plot between the detection time and number of photo-sensors that detect the light, Ms. Keiko Hirata, a Master’s student found a peak, obviously different from the noise in the distribution. It was the exact trace to detect the neutrinos from SN1987A. (A two minutes blank period due to a regular system maintenance is recorded in the plot, at a few minutes before the explosion. If the explosion occurred during this period, Kamiokande could not have detected the SN1987A neutrinos.) After a detailed analysis, it was clear that Kamiokande detected 11 neutrinos for 13 seconds after 16:35:35 on February 23, 1987.

THe magnetic tape recorded SN1987A data

The printout of Kamiokande data and the envelope which stores the printout in. “Keep carefully Y.T.” written by Prof. Youji Totsuka.

The printout of the data. Horizontal axis shows time (from right to left and one line as 10 seconds) and the vertical axis shows the number of hit photo-sensors of each event (approximately proportional to the energy of the event). The obvious peak is the signal of neutrinos from SN1987A. The blank period due to the detector maintainance was recorded a few minutes before the signal.

When Prof. Nakahata finished the analysis and reported to Prof. Koshiba on the morning of March 2, Prof. Koshiba instructed him to investigate the entire data for the presence of similar signals. Under a gag rule, researchers analyzed the 43 days data of Kamiokande on March 2 to March 6, and obtained conclusive evidence that the occurrence of the peak was only from the signal of the supernova SN1987A; further, they published these findings as an article. Here are the the signatures of researchers who wrote the article.

The subsequent development of neutrino research

The Kamiokande’s detection of the supernova neutrinos became a trigger to recognize the importance of neutrino research, and the construction of Super-Kamiokande, whose volume is about 20 times larger than that of Kamiokande, was approved. Super-Kamiokande started observation from 1996 and discovered the neutrino oscillation in 1998. In 2015, Prof. Takaaki Kajita was awarded the Nobel Prize in Physics for this achievement. SN1987A made a worldwide breakthrough in neutrino research, including the K2K experiment, T2K experiment and KamLAND experiment.

If a supernova explosion in our galaxy occurs now, Super-Kamiokande will detect approximately 8,000 neutrinos, almost 1000 times greater than those detected 30 years ago. Further, it is expected that the detailed mechanism of supernova explosion will be revealed and we will understand the stars or our universe in depth. In our galaxy, the supernova explosion is expected to occur once in every 30-50 years. It may occur at this very moment. The neutrinos from the supernova will be detected in mere 10 seconds. Super-Kamiokande continues the observation and will not miss any explosion moment.

Source

Nine facts about neutrinos

Images: Kamioka Observatory,

“Why is there a blue bridge of stars across the center of this galaxy cluster? First and foremost the cluster, designated SDSS J1531+3414, contains many large yellow elliptical galaxies. The cluster’s center, as pictured above by the Hubble Space Telescope, is surrounded by many unusual, thin, and curving blue filaments that are actually galaxies far in the distance whose images have become magnified and elongated by the gravitational lens effect of the massive cluster. More unusual, however, is a squiggly blue filament near the two large elliptical galaxies at the cluster center. Close inspection of the filament indicates that it is most likely a bridge created by tidal effects between the two merging central elliptical galaxies rather than a background galaxy with an image distorted by gravitational lensing. The knots in the bridge are condensation regions that glow blue from the light of massive young stars. The central cluster region will likely undergo continued study as its uniqueness makes it an interesting laboratory of star formation.”

via APOD/NASA;  Image Credit: NASA, ESA, G. Tremblay (ESO) et al.; Acknowledgment: Hubble Heritage Team (STScI/AURA) - ESA/Hubble Collaboration

Well-explained, as always! 😊

How Far Could A Human Travel In A Constantly-Accelerating Rocket Ship?

“Imagine that we could constantly accelerate at the same rate as Earth’s gravitational pull, 9.8 m/s2, indefinitely. While you’d initially speed up, you’ll rapidly approach the speed of light. Owing to Einstein’s Special Relativity, time will dilate and lengths will contract. As you continue to accelerate, the distances and travel times to faraway destinations will plummet. At the halfway mark, simply reverse your thrust to accelerate in the opposite direction for the remaining journey. “

If you wanted to travel to a star that was 100 light-years away, you might think it would take you at least 100 years to get there. That might be true from the perspective of someone who remains on Earth, but for an astronaut who journeyed there at close to the speed of light, Einstein’s Special Relativity tells you that it would take far less than a century of travel. In fact, if you could accelerate at a constant rate, you could pretty much reach anywhere you wanted within 15 billion light-years of us within a human lifetime.

I even went and did the math for you here. Don’t be afraid to see how far a human could travel if we had the dream technology to get us there!

2020 February 19

UGC 12591: The Fastest Rotating Galaxy Known Image Credit: NASA, ESA, Hubble; Processing & Copyright: Leo Shatz

Explanation: Why does this galaxy spin so fast? To start, even identifying which type of galaxy UGC 12591 is difficult – featured on the lower left, it has dark dust lanes like a spiral galaxy but a large diffuse bulge of stars like a lenticular. Surprisingly observations show that UGC 12591 spins at about 480 km/sec, almost twice as fast as our Milky Way, and the fastest rotation rate yet measured. The mass needed to hold together a galaxy spinning this fast is several times the mass of our Milky Way Galaxy. Progenitor scenarios for UGC 12591 include slow growth by accreting ambient matter, or rapid growth through a recent galaxy collision or collisions – future observations may tell. The light we see today from UGC 12591 left about 400 million years ago, when trees were first developing on Earth.

∞ Source: apod.nasa.gov/apod/ap200219.html

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